As many people here know, if you're going to go car-free, you need to figure out a practical way to haul stuff around. I've never tried an Extracycle, so I can't speak intelligently about that, but I have tried trailers, and for hauling heavy stuff, they work extremely well. However, trailers aren't something I want to have attached to my bike every day, so unless the load is excessive, I just won't use one. For daily types of loads (groceries, papers from work, extra clothes during unpredictable spring weather, beer, etc.), I can think of three common methods, all of which I've tried: messenger bags, backpacks, and panniers. Personally, I don't think much of messenger bags, and backpacks and panniers each have their advantages and disadvantages, depending on what you need. Right now, I'm using panniers again, because even though they utterly destroy one's ability to crank hard off the seat or to lean hard on turns, they're simply more practical than anything else I've tried for getting beer back from the store.
What do you think?